1. Field of the Invention
The invention relates to a variable valve gear for internal combustion engines.
2. The Prior Art
A device for variable activation of valves by cams is described in German Patent No. DE 100 61 618 B4. This device is disposed in a cylinder head with a camshaft that is mounted in a fixed position, with valves that close by means of spring force, and together with a stroke transfer arrangement assigned to each of the valves, is guided in the cylinder head in a fixed position. An element that is adjustable for valve stroke adjustment is disposed in the cylinder head, mounted in a fixed position but so as to pivot. It has a supporting cam segment and a controlling cam segment, which run one after the other in an axial plane. An intermediate element is prismatically supported on the element that can be changed in its position, both on the supporting cam segment and the controlling cam segment, with a non-positive lock, and is guided to pivot and glide on the two cam segments in this connection, during the stroke movement. Furthermore, the intermediate element engages one of the cams of the camshaft as well as with a stroke transfer arrangement for a valve. The controlling cam segment determines the movement path of the intermediate element during the stroke of the cam as a function of the pivot position of the changeable element, and thereby the amount of the stroke brought about at the valve by the stroke transfer arrangement.
The design configuration of this embodiment is limited, because the supporting cam segment and the controlling cam segment are disposed running one after the other on the element that can be changed in its position, and therefore a certain distance between the two prismatic engagement lines on the supporting cam segment and the controlling cam segment as well as the intermediate element is necessary.
A variable valve drive for internal combustion engines is described in German Patent Application No. DE 100 31 783 A1, having a valve arrangement moved indirectly by a cam, by way of a rocker or toggle lever mounted directly or indirectly on the cylinder head, so as to pivot. This arrangement has one or more valves that close under the effect of a spring. The rocker or toggle lever engages an intermediate lever that is guided to have a rocking movement. This intermediate lever engages, in sliding or rolling manner, the cam of a camshaft, and a controlling cam segment of a supporting body mounted directly or indirectly on the cylinder head, so as to rotate. The supporting body determines the amount of the valve stroke with its position and the region of a controlling cam segment that becomes effective thereby. The angle position of the supporting body can be adjusted by means of a suitable control and a corresponding actuator.
The complicated and high-effort structure of the adjustment mechanism for changing the stroke of the valve opening range is a disadvantage in this connection. Furthermore, simultaneous adjustment of the valve stroke and the valve opening range cannot be carried out at the same time with the state of the art as described.
In German Patent Application NO. DE 10 2004 010 418.2, which was not published prior to this application, a variable valve gear with an adjustable valve stroke is described, in which forward displacement of the valve opening range automatically takes place in the case of an adjustment in the direction toward a lesser stroke. In this connection, an intermediate lever stands in an effect connection with a pivot lever that activates a valve, by way of a roller disposed on the intermediate lever, and with a supporting cam segment disposed on a pivoting supporting body, and it contacts the cam contour of the camshaft by way of a roller disposed on the intermediate lever. An oscillating guide crank pivots on the intermediate lever, which crank is disposed on a setting arm coupled with the supporting body, in articulated manner.
Introduction of force into the valve gear, which is caused by the displacement of the intermediate lever by the cam contour, is a disadvantage in this connection. Furthermore, this solution requires a relative great construction space.